diff options
Diffstat (limited to 'Documentation/ABI/testing/sysfs-class-bdi')
| -rw-r--r-- | Documentation/ABI/testing/sysfs-class-bdi | 43 |
1 files changed, 15 insertions, 28 deletions
diff --git a/Documentation/ABI/testing/sysfs-class-bdi b/Documentation/ABI/testing/sysfs-class-bdi index c55e811ca18..5ac1e01bbd4 100644 --- a/Documentation/ABI/testing/sysfs-class-bdi +++ b/Documentation/ABI/testing/sysfs-class-bdi @@ -3,8 +3,8 @@ Date: January 2008 Contact: Peter Zijlstra <a.p.zijlstra@chello.nl> Description: -Provide a place in sysfs for the backing_dev_info object. -This allows us to see and set the various BDI specific variables. +Provide a place in sysfs for the backing_dev_info object. This allows +setting and retrieving various BDI specific variables. The <bdi> identifier can be either of the following: @@ -26,34 +26,21 @@ read_ahead_kb (read-write) Size of the read-ahead window in kilobytes -reclaimable_kb (read-only) - - Reclaimable (dirty or unstable) memory destined for writeback - to this device - -writeback_kb (read-only) - - Memory currently under writeback to this device - -dirty_kb (read-only) - - Global threshold for reclaimable + writeback memory - -bdi_dirty_kb (read-only) - - Current threshold on this BDI for reclaimable + writeback - memory - min_ratio (read-write) - Minimal percentage of global dirty threshold allocated to this - bdi. If the value written to this file would make the the sum - of all min_ratio values exceed 100, then EINVAL is returned. - If min_ratio would become larger than the current max_ratio, - then also EINVAL is returned. The default is zero + Under normal circumstances each device is given a part of the + total write-back cache that relates to its current average + writeout speed in relation to the other devices. + + The 'min_ratio' parameter allows assigning a minimum + percentage of the write-back cache to a particular device. + For example, this is useful for providing a minimum QoS. max_ratio (read-write) - Maximal percentage of global dirty threshold allocated to this - bdi. If max_ratio would become smaller than the current - min_ratio, then EINVAL is returned. The default is 100 + Allows limiting a particular device to use not more than the + given percentage of the write-back cache. This is useful in + situations where we want to avoid one device taking all or + most of the write-back cache. For example in case of an NFS + mount that is prone to get stuck, or a FUSE mount which cannot + be trusted to play fair. |